The present invention relates to an information transmission system, and more particularly a system for transmitting the visible images such as letters, pictures and the like represented in the binary coded signals.
For example, in facsimile the blackness of elementary areas of a fixed image or subject copy is converted into the binary coded electrical pulses or bits. That is, the image or subject copy is sequentially scanned with a predetermined scanning line width to be converted into the corresponding electrical video signals which in turn are sampled with an appropriate interval in order to convert them into the binary coded electrical signals. The binary coded electrical signals are then transmitted by wire or wireless to a receiving station, wherein the received signals are demodulated to reproduce the visible image on a record sheet.
The system for transmitting all of the binary coded electrical signals by carrier waves has a defect that the transmission time becomes longer. For example, assume that a subject copy 210 by 297 mm is transversely, sequentially scanned with a scanning line of three-lines per milimeter, and the video signals per scanning line are sampled at 1,024 points to convert them into the binary coded electrical signals. In this case, the blackness of elemental areas in each scanning line are converted into 1,024 bits so that when the telephone line of 2,400 bauds is used, it takes about 6 to 10 minutes to transmit the above subject copy.
When the subject copy is scanned to be converted into the binary coded electrical signals, it is rather rare that the signals representing the black and white are alternately generated at an extremely high frequency. In practice, one binary signals representing black or white are generated in succession. Therefore, assume that ten signals representing for example "1" are generated in succession, and then fifty signals representing "0" are generated in succession. Then, only four bits are required to represent the "1" pulse train, whereas six bits are required to represent the "0" pulse train when the binary number is used. Therefore, it is readily seen that a number of bits to be transmitted and hence the transmission time can be remarkably reduced when the "1" or "0" signal pulse train is represented by the binary number in the manner described above as compared with the case in which every bit of the binary coded signals is transmitted. Various prior art information systems which intend to minimize the transmission time, are all based on the above described principle.
Recently attempts have been made to couple a transmitter station of facsimile to a receiving station by a low-speed telephone line system, but the satisfactory reduction in transmission time cannot be achieved when the binary coded signals are compressed in the manner described above.
Accordingly, one of the objects of the present invention is to provide an improved information transmission system by which the transmission time can be reduced to such an extent hitherto unattained by the prior art system.
When the subject copy to be transmitted consists of letters, pictures or the like, the mutual relation or similarity between the bit patterns of the adjacent scanning lines are in general very high. In some cases, the two bit patterns are completely similar or only a few bits are different. The binary-coded-electrical-signal compression in accordance with the present invention is based upon this observed fact.
According to one embodiment of the present invention, every bit in a bit pattern (to be referred to as an old bit pattern) of a scanning line is compared with associated bit in a bit pattern (to be referred to as a new bit pattern) of the next scanning line. When the old and new bit patterns are coincident with each other, an EQL code signal representing that the new bit pattern is identical or coincident with the old bit pattern, is transmitted instead of the new bit pattern. When the mutual relation or similarity between the old and new bit patterns is higher than a predetermined degree; that is, when the old and new bit patterns are different only in a limited number of bit positions, an ANL (analogous) code signal representing the higher similarity therebetween is transmitted, and the address signals follow which represent the bit positions of the old and new bit patterns only at which they are different. When the old and new bit patterns are entirely or widely different, a NEW code signal representing their desimilarity is transmitted, and followed by the new bit pattern. At a receiving station, the code signals are decoded first. When the EQL code signal is decoded, the old bit pattern previously stored in for example a shift register, is used as the new bit pattern. When the ANL code signal is detected, the address signals following the ANL code signal designate the positions of the bits of the old bit pattern at which the bits must be inverted in polarity or level so that the new bit pattern may be reproduced. When the NEW code is detected, the new bit pattern is used as it is. In like manner, the binary coded bit patterns are compressed and transmitted at the transmitting station, and the received signals are reproduced in the original bit patterns at the receiving station.
The similarity or mutual relation between the bit patterns of the adjacent scanning lines becomes higher as the scanning line width is decreased. In other words, the higher the resolution is desired, the higher the similarity or mutual relation must become. Therefore, the advantages of the information transmission system in accordance with the present invention becomes more pronounced as the higher resolution is required because the bit pattern compression effect and hence the reduction in information transmission time are enhanced.
The above and other objects, features and advantages of the present invention become more apparent from the following description of the preferred embodiment thereof taken in conjunction with the accompanying drawing.